Published French patent No. 2319233, corresponding to U.S. Pat. No. 4,101,793, in the name of ALSTHOM and Electricite de France describes cooling the superconductor of a cryoalternator by a flow of helium at a pressure higher than its critical pressure and at a temperature close to 4.degree. K., said helium flowing round a circuit from a helium refrigerator, and with the helium being returned to the inlet side of the refrigerator after being partially heated by contact with the rotor.
The above patent does not describe a stator which is also superconducting, but under such circumstances it would be normal to provide a second parallel circuit for cooling the stator.
Such a cooling system is relatively complex and expensive, and requires a system of channels for conveying a flow of helium through the stator windings, which channels are of larger size than those used for the rotor.
The aim of the present invention is to provide a synchronous machine having superconductive stator and rotor windings and including a cooling system which is simpler and cheaper.